This invention relates to an immersion lithography system, such as described in WO99/49504, having a fluid material supplied into the space between a workpiece such as a wafer and the last-stage optical member such as a lens of the optical system for projecting the image of a reticle onto the workpiece. The supplied fluid material may be pure water and its presence improves the performance of the optical system and the quality of the exposure.
The fluid material thus supplied into the space between the workpiece and the last-stage optical member tends to rise in temperature due to the radiation energy from the optical system, thereby causing its coefficient of refraction to change. If the fluid material remains in contact with the optical member and the workpiece over an extended period of time, furthermore, the fluid material tends to become polluted, and this also affects its coefficient of refraction. Also the fluid material tends to leak out of the space between the workpiece and the last-stage optical member because the workpiece is moved relative to the last-stage optical member. For these reasons, an immersion lithography system must be provided with an efficient fluid control system for constantly replenishing the lithography fluid.
A problem associated with such a fluid control system for an immersion lithography apparatus is how to control, or contain, the fluid material with which the space between the last-stage optical member and the workpiece is filled.